Method for removing scale deposits



United States Patent 3,447,963 METHOD FOR REMOVING SCALE DEPOSITS Joseph W. Callahan, Sulphur, L2,, assignor to Chemical Cleaning and Equipment Service, Inc., Houston, Tex., a corporation of Texas No Drawing. Filed Oct. 4, 1965, Ser. No. 492,856 Int. Cl. 1308b 3/04 US. Cl. 134-2 3 Claims ABSTRACT OF THE DISCLOSURE Method for removing scale deposits, and particularly scale deposits on sugar mill equipment, using potassium hydroxide having a concentration of from about 25% to about 60% and at a temperature in a range from about 180 F. to about 235 F. and effecting such removal in a reasonable time.

In the past, the sugar refining industry has encountered a number of problems in connection with scale deposits formed on the sugar mill equipment such as the lines, evaporator tubes and boilers. Such scale deposits rapidly build up to substantial thicknesses and if allowed to remain on the equipment, the effectiveness of the equipment is seriously impaired. Heretofore, cleaning methods for the removal of such scale deposits have involved multistage cleaning operations, including the use of acid. Since the sugar mill equipment often employs copper and other metals which are corroded by the acid, the use of acid has been undesriable but it nevertheless has been used because it was believed to be necessary for effective cleaning. Furthermore, such previously known cleaning methods required excessive down-time, that is, time during which the equipment was out of operation for cleaning, such down-time often being as much as eight hours or more, with a resultant loss in valuable production time.

It is therefore an object of this invention to provide a new and improved method for chemically cleaning sugar mill equipment by removing the scale deposits therefrom, wherein a minimum of down-time is required.

An important object of this invention is to provide a new and improved method of chemically removing scale deposits wherein the use of acids corrosive to the equipment having the scale deposits thereon is eliminated.

Another object of this invention is to provide a new and improved method of chemically removing scale de posits wherein concentrated potassium hydroxide is used as the reaction chemical with appropriate heat in a single cleaning stage, and wherein such potassium hydroxide is subsequently recovered for re-use without any substantial loss thereof. I

The preferred embodiment of this invention will be described hereinafter, together with other features thereof, and additional objects will become evident from such description.

The invention will be more readily understood from a reading of the following specification, wherein an example of the invention is described.

Briefly, the method of this invention relates to the cleaning of equipment such as used in sugar mills so as to remove scale deposits therefrom. Quite unexpectedly, it has been found that such scale deposits can be removed in a single stage cleaning treatment with concentrated potassium hydroxide under certain conditions as explained more in detail hereinafter, with the potassium hydroxide being re-usa'ble without any substantial loss in the process. Futhermore, the method or process of this invention has been found to be far more effective and the down-time of the equipment during the cleaning operations has been reduced to a fraction of the time required with prior art methods.

Sugar mill equipment includes the sugar evaporators, connecting flow lines, boilers, and other related equipment. During the use of such equipment, scale deposits build up on the equipment, the presence of which interferes with the heat transfer, fluid flow and general efiiciency of the sugar refining process. By way of example, the following examples show typical compositions of sugar mill scale as found in the evaporators of such sugar mill equipment:

Example 1 Percent Total sulphates as S0,, .37

Total sugars, as dextrose 19.28

Ordinary chemicals such as caustic soda, hydrochloric acid and even the two in sequence are only partially effective in removing such scale deposits. Furthermore, the use of such ordinary chemicals requires that the equipment be out of service for extended periods of time. For example, it is not unusual for sugar mill equipment to be out of use by reason of the cleaning operation for periods of time between three and eight hours, with results that have never been better than about eighty percent effective, using such prior art chemicals and methods.

However, with the present invention, as will be more evident hereinafter, it has been found that sugar mill scale deposits of the types given by way of example above, have been removed in periods of time from about fifteen minutes to about one hour, and such scale deposits have been completely removed, even from the tube sections of the evaporators, which is generally considered to be the most difiicult scale to remove. Such sugar mill scales will vary in thickness, generally from about one sixteenth of an inch in thickness to about one-half inch in thickness.

In carrying out the method of this invention, the cleaning reagent is preferably entirely potassium hydroxide in concentrated form, although it may have other additives therewith so long as they do not interfere with the functioning of the potassium hydroxide. To be effective in carrying out the method of this invention, the potassium hyldroxide should have a concentration of from about about twenty-five percent to about sixty percent by weight in water. Thus, to make up a twenty-five percent potassium hydroxide solution, twenty-five pounds of flake potassium hydroxide are dissolved in water to make up one hundred pounds of total solution. The optimum concentration of potassium hydroxide is forty-five percent by weight.

Such concentrated potassium hydroxide is contacted with the sugar mill scale deposit in the evaporators or flow lines connected therewith, preferably by pumping the cleaning reagent of potassium hydroxide through the lines and tubes of the evaporators. In order to provide a continuous system for treatment of the evaporator or evaporators with the cleaning reagent, the potassium hydroxide is initially supplied from a source of supply such as a tank having the potassium hydroxide therein and to which a pump is connected for pumping the potassium hydroxide through the lines and tubes of the evaporator. The potassium hydroxide is returned to the supply at the tank for subsequent circulation. Normally, as will be more evident hereinafter, an intermediate settling tank for separation of solids from the potassium hydroxide is employed in the system prior to the return of the potassium hydroxide to the supply tank.

While the cleaning reagent is being circulated through the lines and tubes of the evaporator, heat is supplied to the cleaning reagent by applying steam to the shell side of the evaporator, that is, externally of the tubes and lines through which the cleaning reagent is being circulated. Such heat is transferred to the cleaning reagent to raise its temperature to a range of from about 180 F. to about 235 F. The optimum temperature range is preferably from about 190 F. to about 220 F. for such chemical reagent while it is in contact with the scale deposit in the evaporator. By way of specific example, the cleaning reagent in the lines and tubes of the evaporator during cleaning action would preferably be at about 200 F. It will be appreciated that the potassium hydroxide may be heated to the desired temperature prior to introducing it into the evaporator, or the heat can be supplied internally of the fluid with steam or other heating means while the cleaning reagent is in the evaporator under certain conditions.

When a boiler is being cleaned, the cleaning solution is normally heated in the boiler by using ten percent of the rated steam pressure for the boiler to raise the temperature of the cleaning reagent accordingly. For example, if the boiler is a five hundred pound rated steam pressure boiler, the boiler is closed in, and ten percent of such steam pressure, or fifty pounds of steam pressure is introduced for obtaining the desired temperature of the cleaning reagent. Also, the introduction of the steam directly into the cleaning reagent serves to obtain a certain amount of agitation of the cleaning reagent for facilitating the release of the scale deposit from the equipment.

When the cleaning reagent is used in the boiler of the sugar mill equipment, it is allowed to soak therein for a period of time, approximately fifteen minutes to one hour, rather than being circulated therethrough, so that the steam pressure can be fully utilized.

The potassium hydroxide disintegrates the sugar mill scale deposit on the equipment in the evaporator and in the boiler and in the other equipment related thereto so that such scale deposit is released from the metal surfaces of such equipment. Thereafter, by simply rinsing the equipment with water, the scale is washed free of the equipment to leave the equipment completely free, or substantially completely free, of the scale deposit.

Quite unexpectedly, it has been found that the scale deposit apparently goes into a temporary state of solution in the cleaning reagent so that it is released from the equipment and can be removed from the equipment to a remote point for the separation of solids. The scale deposit remains in solution only long enough for it to be removed and then it begins to settle out as a precipitate which is insoluble in the cleaning reagent. Such precipitate is flocculant and constitutes a relatively light mass which settles to the bottom and separates from the cleaning reagent. The cleaning reagent can then be pumped otf as the supernatant liquid for subsequent use since it is at the same, or substantially the same, concentration as it previously was prior to the cleaning operation. Thus, there is no loss of the potassium hydroxide in the cleaning operation so that the potassium hydroxide may be re-used repeatedly for cleaning various types of equipment. It will be understood that although the invention hereof is directed to a cleaning method for removing scale deposits in sugar mill equipment, the invention is not to be limited thereto.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the details of the described invention may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

1. A method of removing scale deposits from sugar mill equipment, comprising the steps of,

(a) contacting scale deposit on sugar mill equipment with a cleaning reagent including potassium hydroxide having a concentration of from about 25% to about (b) heating the potassium hydroxide so that it is at a temperature of from about 180 F. to about 235 F. While contacting the scale deposit, and

(c) thereafter rinsing the equipment with liquid to wash the scale deposit from the equipment.

2. A method of removing scale deposits from sugar mill equipment, comprising the steps of,

(a) contacting scale deposit on sugar mill equipment with a cleaning reagent including potassium hydroxide having a concentration of from about 25 to about 60%,

(b) maintaining the contact of the cleaning reagent with the scale deposit for not more than about one hour to temporarily render the scale deposit soluble in the cleaning reagent so that it releases from the equipment,

(c) thereafter removing the cleaning reagent with the dissolved scale deposit from the equipment on which the scale deposit had been located and allowing the scale deposit to return to an insoluble state for precipitating and separating from the cleaning reagent, and

(d) thereafter separating the cleaning reagent from the precipitated scale deposit.

3. A method of removing scale deposits from sugar mill equipment, comprising the steps of,

(a) contacting scale deposit on sugar mill equipment with a cleaning reagent including potassium hydroxide having a concentration of from about 25% to about 60%,

( b) maintaining the contact of the cleaning reagent with the scale deposit for not more than about one hour at a temperature of from about 180 F. to about 235 F. to temporarily render the scale deposit soluble in the cleaning reagent so that it releases from the equipment,

(c) thereafter removing the cleaning reagent with the dissolved scale deposit from the equipment on which the scale deposit had been located and allowing the scale deposit to return to an insoluble state for precipitating and separating from the cleaning reagent, an

(d) thereafter separating the cleaning reagent from the precipitated scale deposit.

MORRIS O. WOLK, Primary Examiner.

M. D. BURNS, Assistant Examiner.

US. Cl. X.R. 

